1. Field of the Invention
The present invention relates to a distance measurement and photometry device, a distance measurement and photometry method, and an imaging apparatus.
2. Description of the Related Art
Heretofore, in an external measurement type of a distance measurement and photometry device, a device is known that has a pair of distance measurement line sensors and multiple sensors as a photometry sensor (for example, see Japanese Patent No. 4217491). The device has two cameras that comprise a pair of distance measurement line sensors corresponding to a pair of lens, detects a parallax of a subject captured by the two cameras, and measures a distance to a subject by triangulation.
Japanese Patent No. 4217491 describes a pair of distance measurement line sensors and a large sensor as a photometry sensor on a semiconductor chip. Referring to the Japanese Patent No. 4217491, on the semiconductor chip, the center of the large sensor as a photometry sensor is displaced with reference to the line linking the center of one of the pair of distance measurement line sensors and the center of the other of the pair of distance measurement line sensors, so that it can reduce the semiconductor chip size and the size of a distance measurement and photometry device.
Additionally, a distance measurement and photometry device is known that has a pair of distance measurement line sensors, divided into plural areas, and measures a distance to a subject by use of the plural areas. The device measures a distance to a subject again if the electric charge of the camera is not enough, radiates strobe light and fill light while charging electricity of the camera. By doing so, the device can measure a distance to a subject even if it is cloudy. For example, see Japanese Publication No. 2005-227750.
However, Japanese Patent No. 4217491 and Japanese Publication No. 2005-227750 can measure the center part of a view only because they are configured to measure a distance by use of a pair of distance measurement line sensors. In other words, they cannot measure plural distances over a photographing screen entirety. To measure the plural distances, a two-dimensional image sensor is required. When the two-dimensional image sensor is used, an accuracy of measuring a distance needs to be greater than when using the pair of distance measurement line sensors to measure the plural distances over a photographing screen entirety.
The physical characteristics of a two-dimensional image sensor are different from a result of measuring a distance due to the state of lighting environment of a subject. Especially, an accuracy of measuring a distance is affected by a light source, and strongly affected under a lighting environment of fluorescent light.
TABLE 1POWER FREQUENCYUNITED STATES60HzUNITED KINGDOM50HzCHINA50HzJAPAN50/60Hz
TABLE 1 shows differences of power frequencies of commercial power supplies. The power frequencies of commercial power supplies are roughly classified into 50 Hz or 60 Hz.
When a two-dimensional image sensor is used, the image sensor exposes a fixed frame rate as, for example 30 fps (frames per second), and continuously repeats a light-dark cycle due to a timing of exposure.
In general, this phenomenon is called flicker-phenomenon. When a distance is measured by use of a pair of two-dimensional image sensors under a lighting environment in which flicker occurs, due to a timing of exposure, an unevenness of exposure arises because the subject image that is formed in one of the pair of two-dimensional image sensors gets dark or gets light. Therefore, the brightness of the subject images that are formed in the pair of two-dimensional image sensors becomes imbalanced. Even if the pair of two-dimensional image sensors are synchronized with each other and measure a distance, a gap of timing of exposure between the two sensors slightly arises.
Also, when a light source gets dark, the exposure amount of an image sensor needs to be increased. For a two-dimensional image sensor, which is required to synchronize and transfer to each pixel line, the image sensor may only expose a certain amount of frame rate. Therefore, an exposure amount and a frame rate corresponding to a subject need to be varied.